The present invention relates to cationic ruthenium complexes which can be used, for example, as catalysts in metathesis reaction and processes for their preparation.
Olefin metathesis (disproportionation) involves, in its simplest form, a reversible, metal-catalyzed transalkylidenation of olefins by rupture and reformation of carbon-carbon double bonds. In the case of the metathesis of acyclic olefins, a distinction is made, for example, between self-metathesis in which an olefin is transformed into a mixture of two olefins having different molar masses (for example conversion of propene into ethene and 2-butene) and cross-metathesis or cometathesis in which two different olefins react (for example propene with 1-butene to give ethene and 2-pentene). Further application areas of olefin metathesis include syntheses of unsaturated polymers by ring-opening metathesis polymerization (ROMP) of cyclic olefins and the acyclic diene metathesis polymerization (ADMET) of xcex1,xcfx89-dienes. More recent applications concern the selective ring opening of cyclic olefins by means of acyclic olefins, and also ring closure reactions (RCM) by means of which, preferably starting from xcex1,xcfx89-dienes, unsaturated rings of various ring sizes can be prepared.
Suitable catalysts for metathesis reactions are in principle homogeneous and heterogeneous transition metal compounds.
Heterogeneous catalysts, for example molybdenum, tungsten or rhenium oxides on inorganic oxidic supports, have high activity and regenerability in reactions of non-functionalized olefins but often have to be pretreated with an alkylating agent to increase the activity when using finctionalized olefins such as methyl oleate. Olefins having protic functional groups (such as hydroxyl groups, carboxyl groups or amino groups) lead to spontaneous deactivation of the heterogeneous catalyst.
In recent years, increased efforts have been made to prepare homogeneous catalysts which are stable in protic medium and in the presence of atmospheric oxygen. Here, specific ruthenium alkylidene compounds have attracted particular interest. Such complexes and processes for their preparation are known.
WO 93/20111 describes ruthenium- and osmium carbene complexes for olefin metathesis polymerization. The complexes have the structure RuX2(xe2x95x90CHxe2x80x94CHxe2x95x90CR2)L2. Ligands L used are triphenylphosphine and substituted triphenylphosphine. The complexes are prepared, for example, by reacting RuCl2(PPh3)3 with suitable disubstituted cyclopropenes as carbene precursors. However, the synthesis of cyclopropene derivatives involves a number of steps and is of little interest from a commercial point of view.
Similar reactions are described in WO 96/04289. Processes for olefin metathesis polymerization are also mentioned.
Use of such catalysts for peroxide crosslinking of ROMP polymers is described in WO 97/03096.
WO 97/06185 likewise describes metathesis catalysts which are based on ruthenium carbene complexes. Apart from the above-described method, they can also be prepared by reacting RuCI2(PPh3)3 with diazoalkanes. However, handling diazoalkanes constitutes a safety risk, particularly when the process is carried out on an industrial scale.
In addition, the starting materials of the formula RuCl2(PPh3)3 have to be prepared from RuCl33H2O using a large excess of triphenylphosphine. In the catalyst synthesis itself, PPh3 ligands are again lost as a result of ligand replacement. The carbene precursors used require multistage syntheses and do not keep indefinitely.
Organometallics 1996, 15, 1960 to 1962, describes a process for preparing ruthenium complexes in which polymeric [RuCI2(cyclooctadiene)]x is reacted with hydrogen in i-propanol in the presence of phosphine. This eliminates the need for the phosphine replacement. An undefined mixture of products is obtained. In addition, long reaction times are necessary when starting from a polymeric starting material. The cyclooctadiene present in the starting material does not contribute to the reaction and is lost.
J. Chem. Soc. Commun. 1997, 1733 to 1734, describes a synthesis of the methylene complex RuCI2(xe2x95x90CH2)(PCy3)2, which starts from dichloromethane and the ruthenium polyhydride complex RuH2(H2)2(PCy3)2. However, the ruthenium polyhydride complex is difficult to obtain. In addition, long reaction times are necessary.
The above ruthenium(II) alkylidene complexes, like all other known metathesis catalysts containing electron-rich transition metals, are unsuitable, or have only limited suitability, as catalysts for metathesis reactions of electron-poor olefins such as acrylic acid or derivatives thereof.
Catalyst systems based on molybdenum and tungsten have only very limited suitability for metathesis reactions of functionalized olefins. The most active catalysts involving electron-poor transition metals, e.g. the systems of the type (RO)2M(NR)(xe2x95x90CHRxe2x80x2)(Mxe2x95x90Mo, W) described in EP-A-0 218 138, suffer not only from the disadvantage of a low activity in respect of such substrates but also the disadvantage of an extremely high sensitivity to impurities in the feed and are also of no interest from an economic point of view because of their very high preparation costs. In J. Am. Chem. Soc. 1995, 117, 5162 to 5163, Crowe describes the use of these catalysts for mechanistic studies on cross-metathesis reactions of acrylonitrile (H2Cxe2x95x90CHCN) with H2Cxe2x95x90CHR (Rxe2x95x90electron-donating radical) to give NCHCxe2x95x90CHR and H2Cxe2x95x90CH2, which proceed to only moderate conversions even at high catalyst concentration. U.S. Pat. No. 5,621,047 describes the ring-opening cross-metathesis of cyclooctadiene with methyl methacrylate using WCl6/SnMe4 to give oligomers having carboxylic end groups.
Inexpensive catalyst systems which are stable to impurities in the feed and to atmospheric oxygen and are suitable for metathesis reactions in which electron-poor olefins participate are unknown hitherto.
It is an object of the present invention to develop a catalyst system for metathesis reactions of electron-poor olefins to enable metathesis reactions to be carried out on large-volume, basic industrial products such as acrylic acid and derivatives thereof, acrylonitrile, vinyl chloride, vinyl sulfone, etc. Apart from a high activity, a high stability to impurities in the feed and to atmospheric oxygen as well as a long operating life and inexpensive and uncomplicated synthesis from readily available raw materials should be realized.
We have found that this object is achieved by catalyst systems comprising as active components cationic ruthenium complexes of the formula A (cationic carbyne complexes) or B (cationic carbene complexes) or mixtures in which these are present, 
where B may be stabilized by a further ligand L4. In the structures A and B, xe2x80x94C
Xxe2x88x92 is an anion which does not coordinate or coordinates only weakly to the metal center, for example a complex anion from main groups III to VII of the Periodic Table of the Elements, e.g. BRxe2x80x34xe2x88x92(Rxe2x80x3=F or phenyl which may be substituted by one or more fluorine atoms or by polyfluorinated or perfluorinated C1-C6-alkyl radicals, for example C6H5xe2x88x92nFn where n=1 to 5), PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, ClO4xe2x88x92, CF3SO3xe2x88x92 or FSO3xe2x88x92,
Y is a monodentate or multidentate anionic ligand,
R and Rxe2x80x2 are each, independently of one another, hydrogen or a substituted or unsubstituted C1-C20-alkyl, C6-C20-aryl or C7-C20-alkylaryl or aralkyl radical,
L1, L2, L3 and L4 are, independently of one another, uncharged electron donor ligands, preferably nitrogen donors, for example amines and pyridines, phosphines, arsines, stibines, bearing at least two bulky radicals such as i-propyl, t-butyl, cyclopentyl, cyclohexyl, methyl or the like, or else xcfx80-coordinated olefins or solvent molecules.
The groups preferably have the following meanings:
Xxe2x88x92 is BRxe2x80x34xe2x88x92 where Rxe2x80x3=F or C6H3 (m-CF3)2,
Y is halogen, preferably chlorine, or OR where Rxe2x95x90C1-C6-alkyl, C6-C12-aryl, preferably phenoxide,
R is H,
Rxe2x80x2 is C1-C6-alkyl, C6-C12-aryl, C7-C20-aralkyl, preferably methyl or benzyl,
L1, L2 are phosphines bearing at least two bulky radicals,
L3, L4 are cyclic or acyclic ethers or tertiary amines such as NMe2phenyl, NMe3, NEt3.
The synthesis of the active components A and/or B or of mixtures in which these active components are present can be carried out starting from numerous organometallic starting materials, for example
by reacting hydrido(vinylidene) complexes of the type RuY(H)(xe2x95x90Cxe2x95x90CHR)L1L2, which can be synthesized by reacting RuCIH(H2)L1L2 with terminal alkynes HCCR, with R+Xxe2x88x92, where Xxe2x88x92is a non-coordinating or weakly coordinating anion. RuCIH(H2)L2 can here be prepared as described in the literature, for example from the polymeric ruthenium precursor [RuCl2(COD)]x(COD=cyclooctadiene) in i-propanol in the presence of L under a hydrogen atmosphere (Werner et al., Organometallics 1996,15, 1960 to 1962) or starting from the same starting material in sec-butanol in the presence of L and tertiary amines (NEt3) under a hydrogen atmosphere (Grubbs et al., Organometallics 1997, 16, 3867 to 3869). RuClH(H2)L2 is also obtainable starting from RuCl3.H2O in THF by reaction with L in the presence of activated magnesium under a hydrogen atmosphere (BASF AG, DE-A-198 00 934 which has earlier priority but is not a prior publication) and is preferably reacted in situ with 1-alkynes to give the corresponding hydrido(chloro)vinylidene complexes RuClH(xe2x95x90Cxe2x95x90CHR)L2. The latter can be isolated or react in situ with H+Xxe2x88x92(Xxe2x88x92=non-coordinating anion) to give the active components A and/or B of the present invention.
By reacting compounds of the type RuYYxe2x80x2(xe2x95x90CHR)L1L2 (where Y can be the same as Yxe2x80x2) with R+Xxe2x88x92, where Xxe2x88x92 is a non-coordinating or weakly coordinating anion. Mixed-anion alkylidene complexes RuXY(xe2x95x90CHCH2R)L2 can be prepared as described in DE-A-198 00 934 starting from RuXH(xe2x95x90Cxe2x95x90CHR)L2.
By reacting compounds of the type RuYYxe2x80x2(xe2x95x90CHR)L1L2 with anion-abstracting abstracting metal salts M+Xxe2x88x92 or Lewis acids such as BF3 of AlCl3 in the presence of a ligand L3, where Xxe2x88x92 is a non-coordinating or only weakly coordinating anion and the anionic ligands Y and Yxe2x80x2 can be identical or different. MX can be, for example, AgPF4, AgB(C5F5)4, AgPF6 or AgSbF6R+Xxe2x88x92, M+Xxe2x88x92and the corresponding Lewis acids are preferably used in a molar ratio, based on the organometallic starting material, of from 1:10 to 1000:1.
Reactions to give the active components A and/or B are preferably carried out in organic solvents under an inert gas atmosphere, preferably in solvents which can stabilize an unsaturated metal center by coordination, for example aliphatic or cyclic ethers such as dioxane or THF, amines, DMSO, nitriles, phosphines, arsines, stibines, water, olefins or other two-electron donors. The reaction is preferably carried out in THF at from xe2x88x92100 to +100xc2x0 C., preferably from xe2x88x9280 to xe2x88x9240xc2x0 C., and pressures of from 1 mbar to 100 bar, preferably from 0.5 to 5 bar.
The reaction can be carried out using one or more molar equivalents of R+Xxe2x88x92. L1xe2x88x923RX formed when using excess R+Xxe2x88x92does not adversely affect the reaction. The compositions comprising the active components A and/or B obtained in this way can be used in situ as a highly active metathesis catalyst system or can be stored at low temperatures under an inert gas atmosphere. If desired, the active components A or B are used in isolated form.
The reaction is generally complete after from 1 second to 10 hours, preferably after from 3 seconds to 1 hour. Suitable reaction vessels are glass or steel vessels in general, if desired lined with ceramic.
The components A and/or B or mixtures in which these components are present are highly active metathesis catalysts for linear and cyclic olefins.
The catalyst systems can be used, inter alia, for
self-metathesis of an olefin or cross-metathesis or two or more olefins,
ring-opening metathesis polymerization (ROMP) of cyclic olefins,
selective ring opening of cyclic olefins using acyclic olefins,
acyclic diene metathesis polymerization (ADMET),
ring-closure metathesis (RCM)
and numerous metathesis variants.
In contrast to RuCl2(xe2x95x90CHR)L2, use of these catalyst systems enables for the first time electron-poor olefins of the type RaRbCxe2x95x90CRCZ, where Ra, Rb, Rc are, independently of one another, hydrogen, C1-C12-alkyl or C6-C12-aryl and Z is an electron-withdrawing radical such as CO2Rd, CONH2, COX, CN where X is halogen and Rd is hydrogen, C1-C12-alkyl or C1-C12-aryl, to be reacted efficiently and with very high activity even under mild reaction conditions. Examples which may be mentioned are acrylic acid and its derivatives, fumaric and maleic esters, maleic anhydride, vinyl chloride, methyl vinyl ketone and others.
The invention is illustrated by the examples below.